subtree(users/wpcarro): docking briefcase at '24f5a642' r/3226

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c09813172c79820bcf526bb10cf4208
git-subtree-split: 24f5a642af3aa1627bbff977f0a101907a02c69f
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

1 files changed, 48 insertions, 0 deletions

diff --git a/users/wpcarro/scratch/data_structures_and_algorithms/dijkstra-shortest-path.py b/users/wpcarro/scratch/data_structures_and_algorithms/dijkstra-shortest-path.py
new file mode 100644
index 000000000000..03907f604044
--- /dev/null
+++ b/users/wpcarro/scratch/data_structures_and_algorithms/dijkstra-shortest-path.py
@@ -0,0 +1,48 @@
+from collections import deque
+from heapq import heappush, heappop
+from fixtures import weighted_graph
+
+
+def put(t, x, xs):
+    if t == 'stack':
+        return xs.append(x)
+    if t == 'queue':
+        return xs.append(x)
+    if t == 'priority':
+        return heappush(xs, x)
+
+
+def pop(t, xs):
+    if t == 'stack':
+        return xs.pop()
+    if t == 'queue':
+        return xs.popleft()
+    if t == 'priority':
+        return heappop(xs)
+
+
+# shortest_path :: Vertex -> Vertex -> Graph -> [Vertex]
+def shortest_path(a, b, g):
+    """Returns the shortest path from vertex a to vertex b in graph g."""
+    t = 'priority'
+    xs = []
+    seen = set()
+    # Map(Weight, [Vertex])
+    m = {}
+
+    put(t, (0, [a], a), xs)
+
+    while xs:
+        w0, path, v = pop(t, xs)
+
+        seen.add(v)
+        if v == b:
+            m[w0] = path
+        for w1, x in g.get(v):
+            if x not in seen:
+                put(t, (w0 + w1, path + [x], x), xs)
+
+    return m
+
+
+print(shortest_path('a', 'f', graph_a))